In such a blade carrying assembly, the wiper arm conventionally includes a shroud portion at its inner end. The shroud portion is normally of a generally U-shaped cross section, with the sides of the shroud portion flanking the coupling head, and a pivot, which is secured by riveting, providing the necessary articulation between the shroud portion and the coupling head.
At the end of the wiper arm opposite that to which the coupling head is attached, a windshield wiper blade, for sweeping the windshield, is attached by means of a hooked connection. To optimise the operating conditions for sweeping the windshield, it is necessary to provide means for applying a pressure to urge the wiper blade towards the windshield. For this purpose a traction spring is fitted in such a way as to bias the wiper arm towards the coupling head, and therefore towards the windshield.
When replacement of the wiper blade is necessary, or when the blade carrying assembly is to be removed, the arm is swung out, that is to say it is moved to a position in which it is no longer urged against the windshield by the force exerted by the spring. This operation of swinging the wiper out is generally performed by rotating the wiper arm with respect to the coupling head in a direction away from the windshield, and into a position in which the anchor point of the spring on the wiper arm has passed behind (with reference to the windshield) the anchor point of the spring on the coupling head, so that the force exerted by the traction spring then holds the wiper blade away from the windshield.
This method places the wiper arm into a quasi-perpendicular position with respect to the coupling head and therefore with respect to the chassis of the vehicle. In modern vehicles on which the coupling head is placed beneath an edge of the bodywork overlying the hood of the vehicle, this is no longer possible, because with such an arrangement it is only possible to displace the wiper arm a few degrees about the pivot axis coupling the arm to the coupling head.
There is therefore a need to provide an alternative arrangement in which the spring can be prevented from exerting its biassing force within the small range of displacement available for the arm.
It has already been proposed, in patent application No. 35 08542 filed in the Federal Republic of Germany on 9th Mar. 1985, to provide means for transmitting force between the spring and the wiper arm. These force transmitting means comprise a lever on which the spring acts, together with a coupling member between this lever and the wiper arm. The coupling member is actuated in a simple manner so as to separate the lever and the wiper arm. The spring then no longer acts on the arm, so that the latter can be displaced as required. This arrangement, however, has the disadvantage that, since the arm is thus freely rotatable with respect to the coupling head, the person working on the windshield wiper must take care not to allow it to come into contact with the vehicle hood and so run the risk of damaging the paintwork.